The present invention relates to a method of processing images formed with an imaging device, more particularly, to a method of processing images formed with an imaging device by correcting defective pixels in the imaging device.
One of the methods for image acquisition is by using an imaging device that converts light to an electric signal.
Take, for example, an image scanner, facsimile, digital camera, or a video camera; the available method is to record image using a semiconductor light-receiving device (so-called “charge-coupled device,” which is hereinafter sometimes referred to as “CCD”) that converts light to an electric signal.
In other applications such as medical diagnostic imaging and industrial non-destructive testing, the available method is to record a radiation image by first allowing a radiation (e.g. X-rays, α-rays, β-rays, γ-rays, electron beams or uv rays) to pass through the object, causing it to be stored as a record in a storage phosphor sheet (so-called imaging plate), and reading the photostimulated luminescence that is emitted from the storage phosphor sheet.
Another method adopted in these applications such as medical diagnostic imaging and industrial non-destructive testing is to use a radiation image detector which records a radiation image by first allowing a radiation (e.g. X-rays, α-rays, β-rays, γ-rays, electron beams or uv rays) to pass through the object and then picking up the radiation as an electric signal.
An example of this radiation image detector is a device that employs a solid-state radiation detector (so-called “flat panel detector” which is hereinafter sometimes referred to as “FPD”) that picks up the radiation as an electrical image signal.
FPDs are operated by one of two methods, direct and indirect; in the direct method, electron-positive hole pairs (e-h pairs) emitted from a film of photoconductive material such as amorphous selenium upon incidence of a radiation are collected and read as an electric signal, whereby the radiation is “directly” converted to an electric signal: in the indirect method, a phosphor layer (scintillator layer) which is formed of a phosphor that emits light (fluoresces) upon incidence of a radiation is provided such that it converts the radiation to visible light, which is read with a photoelectric transducer, whereby the radiation “as visible light” is converted to an electric signal.
The above-described image recording apparatus using the CCD or the radiation image recording apparatus using the FPD may suffer a deterioration in the quality of images and defective pixels in the CCD or FPD may be mentioned as one of the causes of such deterioration.
To be more specific, not all of the pixels (detecting elements) in the CCD or FPD will output a signal of the right intensity in response to the incident light or radiation (radiation dose) but there exist some pixels which output a signal of either abnormally low or abnormally high value in response to the light or radiation.
These areas (pixels) where defective pixels occur are unable to produce the right image. If the right image cannot be obtained on account of the defective pixels, an especial problem arises in the case where the produced image is to be used as a medical image since this can lead to such a serious trouble as wrong diagnosis.
Hence, in the radiation image recording apparatus, the positions of defective pixels are preliminarily detected on a specified timing and when the radiation image is to be recorded, the result of detection of the defective pixels is relied upon to perform defective pixel correction, in which pixels adjacent a defective pixel (or the relevant image data) are used to correct the defective pixels, and the radiation image that has been corrected for the defective pixels is displayed as the diagnostic image or the like, or reproduced as a print.
The following methods have been proposed with a view to correcting the image detects due to the above-described defects in the imaging device (see Patent Documents 1 and 2).
JP3-279936 A describes a radiation image display method characterized in that when a storage phosphor sheet in which a radiation image has been stored as a record is irradiated with exciting light and the resulting photostimulated luminescence that is emitted from the storage phosphor sheet is captured to obtain an image signal which is relied upon to display a visible image, a singular point position signal that represents the position of a singular point due to a defect on the surface or in the bulk of the storage phosphor sheet which appears in the radiation image that is carried by the image signal is entered, an interpolating operation is performed based on the image signals corresponding to pixels adjacent the singular point to thereby determine an interpolated image signal corresponding to the singular point, the interpolated signal is substituted for the image signal corresponding to the singular point, and a visible image is displayed based on the substituted image signal.
JP3-279936 A also describes one-dimensional interpolation that is performed as a method of correcting detective pixels.
JP2006-60678 A mainly relates to image processing as applicable to digital cameras and describes an imaging apparatus which, when a continuous shooting mode or a video shooting mode is set that requires high-speed image data processing which puts greater emphasis on speed than on image quality compared with a still image shooting mode for obtaining image data for still image, the image data corresponding to each of the defective pixels within the image data for the recorded image that have occurred at consecutive positions is subjected to a defective pixel correcting treatment based on the position information about the defective pixels that is loaded in a continuous defect correcting LUT 66A stored in a high-speed memory SRAM 66 whereas when a still image shooting mode that requires acquisition of image data of higher quality than in the continuous shooting mode or the video shooting mode is set, image data associated with the position information about all defective pixels within the image data for the recorded image is corrected based on two kinds of position information, one being the position information about the defective pixels that is loaded in an single defect correcting LUT 78A stored in memory SDRAM 78 which has a lower access speed than SRAM 66, and the other being the position information about the defective pixels that is loaded in continuous defect correcting LUT 66A stored in high-speed memory SRAM 66.